Integrated quantum light sources for continuous variable systems
Final Report Abstract
The project goal was to develop integrated resonator systems as highly efficient SHG and squeezed light sources. The devices were to be realised in the titanium indiffused lithium niobate waveguide platform, which provide a low-loss platform with access to the electro-optic effect for cavity length control via integrated phase modulators. Integrated phase modulators allow for stabilisation of the cavity resonance to the incident laser frequency, a critical requirement for any network application. Initial research activities included the modelling of the intended devices in order to understand the complex spectral structures that are produced and in order to determine the optimum parameters for device production. This modelling was used to design the optimum resonator parameters for each of the planned devices, taking into account the measured performance (such as the losses and nonlinear interaction strength) of the devices that could be produced. Concurrently, research was undertaken to develop integrated phase modulators on these waveguides. Critically, these modulators should not significantly increase the round-trip losses of the system and, furthermore, the DC-drift effect, an effect due to charge migration in the buffer layer that causes a shift in the set-point of the system with an applied voltage, should be minimised. A key challenge was the development of these electro-optic modulators. A number of waveguide samples were produced with varying buffer layer thicknesses, electrode thicknesses, and adhesion layer materials and thicknesses. Naturally, production of each of these devices requires much preparation and device time, from first producing the waveguide samples and characterising their losses, to finally undergoing the deposition of the desired modulator design. A design was developed that minimised the increase in losses seen after deposition and that were stable at the required high temperature operation, but unfortunately the DC-drift for this design was seen to be significant and limited device performance. A key challenge was to investigate the performance of the integrated modulators when locking the resonance condition of the cavity. Although techniques were used in order to minimise the known effect of DC drift, the effect was still seen to negatively affect device performance. Although this effect alone could, in principle, be compensated for, a higher than expected pi voltage was also observed. These two effects in unison led to reduced device stability over longer periods of time. A number of waveguide resonator sources were produced but many were also damaged through operation owing to the higher than expected observed pi voltages. Higher voltages than were initially desired were applied to some samples in order to fully compensate for the DC drift, however, these increased voltages led to arcing and it was therefore not possible to completely counter the effect of the DC drift. The arcing caused local damage to the waveguides requiring new samples to be produced. Nevertheless, operating at lower voltages a device stable over tens of minutes was produced and the results have been published. The project was set up to be very ambitious in its goals. The reduced funding as well as the unfortunate coronavirus situation, leading to the closure of the university for many months affected the outcomes of the project. Nevertheless, a number of key results were obtained and the intended outcomes from the project continue to be investigated.
Publications
- "Interferometric method for determining the losses of spatially multi-mode nonlinear waveguides based on second harmonic generation.," Opt. Express 28, 5507-5518 (2020)
M. Santandrea, M. Stefszky, G. Roeland, and C. Silberhorn
(See online at https://doi.org/10.1364/oe.380788) - "Waveguide resonator with an integrated phase modulator for second harmonic generation," Opt. Express 29, 1991-2002 (2021)
M. Stefszky, M. Santandrea, F. vom Bruch, S. Krapick, C. Eigner, R. Ricken, V. Quiring, H. Herrmann, and C. Silberhorn
(See online at https://doi.org/10.1364/oe.412824)
